Method and apparatus for detecting flame with adjustable optical coupling

Abstract

A method of detecting flame within a region where flame is expected. Radiation emissions from the region are measured within selected portions of the visible and infra-red frequency bands. Spectral characteristics of the two measurements, including their auto spectra, coherency and transfer function, are derived. The derived spectral characteristics are compared with prestored spectral signatures representative of the spectral characteristics of radiation emitted from the region within the selected portions of the visible and infra-red frequency bands while known flame conditions prevail within the region--thereby estimating the deviation of the derived spectral characteristics from the prestored spectral signatures. The deviations aforesaid are compared with predetermined threshold alarm values to assess the presence or absence of flame.

We claim: 
     
       1. Flame detection apparatus, comprising: (a) a dual colour sensor for sensing radiation emissions in the visible frequency band from a first zone, for sensing radiation emissions in the infra-red frequency band from a second zone, and for producing first and second output signals representative of said sensed emissions;   (b) a lens optically coupled to said sensor; and,   (c) means for adjusting said optical coupling such that said first and second zones coincide within a selected region and diverge outside said region.   
     
     
       2. Flame detection apparatus as defined in claim 1, further comprising a plurality of said sensors, each optically coupled to said lens at selected lateral displacements off said lens' principal axis. 
     
     
       3. Flame detection apparatus as defined in claim 2, further comprising fibre optic coupling means for optically coupling said lens to said sensors. 
     
     
       4. Flame detection apparatus as defined in claim 3, further comprising cooling means for cooling said lens and said sensors. 
     
     
       5. Flame detection apparatus as defined in claim 4, wherein said means for adjusting said optical coupling between said sensor and said lens comprises a first barrel for mounting said sensors and a second barrel for mounting said lens, said barrels being telescopically interconnected to vary the longitudinal displacement between said sensors and said lens by slidable displacement of said barrels relative to one another. 
     
     
       6. Flame detection apparatus as defined in claim 5, wherein said cooling means comprises an air passage for conveying cooling air through said barrels, over said sensors and said lens. 
     
     
       7. Flame detection apparatus as defined in claim 3, further comprising flexible mounting means for mounting said sensors and said lens to permit flexible displacement of said sensors relative to said lens. 
     
     
       8. Flame detection apparatus as defined in claim 2, wherein said sensors are selected from the group consisting of: (a) silicon lead sulphide sensors;   (b) silicon lead selenide sensors; and,   (c) silicon germanium sensors.   
     
     
       9. Flame detection apparatus as defined in claim 8, wherein said lens is sapphire. 
     
     
       10. Flame detection apparatus as defined in claim 3, wherein said fibre optic coupling means is zirconium fluoride. 
     
     
       11. Flame detection apparatus as defined in claim 2, further comprising aperture restricting means for restricting the apparent diameter of said lens relative to said sensors. 
     
     
       12. Flame detection apparatus as defined in claim 2, further comprising signal processing means for receiving said sensor output signals and for selecting a pair of said signals produced by a selected one of said sensors. 
     
     
       13. Flame detection apparatus as defined in claim 11, wherein said signal processing means further comprises: (a) a multiplexer for receiving said first and second output signals from each of said sensors;   (b) a tone decoder electrically coupled to said multiplexer, said tone decoder for detecting preselected tone signals, each tone signal corresponding to one of said sensors, and for applying one of a corresponding number of select signals to said multiplexer upon detection of any of said tone signals to cause said multiplexer to pass said first and second output signals produced by said sensor corresponding to said detected tone signal.   
     
     
       14. Flame detection apparatus as defined in claim 11, wherein said signal processing means further comprises a voltage controlled gain stage for preventing signal saturation when said first and second output signals are produced by bright flame or high flicker flame in said selected region. 
     
     
       15. Flame detection apparatus as defined in claim 11, wherein said signal processing means further comprises filter means for filtering said first and second output signals, said filter means having a frequency proportional gain characteristic.